Microwave heating apparatus

ABSTRACT

A microwave heating apparatus and a method of heating a load using microwaves is disclosed. The microwave heating apparatus comprises a cavity arranged to receive a load, a plurality of feeding ports for feeding microwaves from a plurality of microwave generators to the cavity, and a control unit. The control unit is configured to obtain a desired temperature pattern within the cavity based on information about a plurality of regions of the load. The control unit is also configured to determine a heating pattern comprising zones of different intensities corresponding to the desired temperature pattern, and control at least one of the plurality of microwave generators for providing the heating pattern within the cavity. The apparatus and method may provide heating of a load according to different desired temperatures in various parts of the load.

TECHNICAL FIELD

The present disclosure relates to the field of microwave heating, and inparticular to a microwave heating apparatus for heating a load by meansof microwaves.

BACKGROUND

Microwave ovens usually comprise a cooking chamber in which food isplaced to be heated, a magnetron for generating microwaves and a feedingport for feeding the microwaves into the cavity. A common problemassociated with microwave ovens is that the heating provided by themicrowaves is unevenly distributed within the cavity. This causes someparts of the food to be heated more rapidly than other parts. In otherwords, the heating results in food having regions of differenttemperatures (i.e. being more or less hot). For example, food that hasbeen defrosted in a microwave oven often contains parts which are stillfrozen, while other parts of the food may be really hot. To ensure thatall parts of the food in the microwave oven are properly heated, theuser often heats the food for an extra long time, thereby running therisk of burning parts of the food because of overheating.

Several different approaches have been employed to overcome such aproblem. A more even heating in a microwave oven may for example beobtained by placing the food on a turntable in the cavity. Duringheating, the turntable is rotated, whereby the heating provided by themicrowaves is more evenly distributed in the food. However, the use ofrotating turntables still does not provide sufficient spread of theheating in the food. Another drawback is that the introduction of extramoving parts such as the turntable, and a motor for driving theturntable, increases the risk of malfunction and also makes themicrowave oven more complicated to manufacture.

Another approach for providing a more even heating is described inEP0788296 where a high frequency heating apparatus with local heatingmeans capable of heating an optional portion of the food is disclosed.The local heating means provides a heating position that is changeablein a radial direction so that an optional portion of the food can beheated in association with rotation of a turntable on which the food islocated. A uniform heating distribution of the food may then be obtainedby a combined heating of optional portions. Although this high frequencyheating apparatus may provide better control of the heating than thoseonly using turntables, it is fairly complicated and still requires aturntable and a motor for rotating the turntable.

Thus, there is a need for new apparatus and methods that would overcome,or at least alleviate, some of the above mentioned drawbacks.

SUMMARY

An object of at least some of the embodiments of the present disclosureis to provide a microwave heating apparatus, and a corresponding methodof heating a load using microwaves, with improved control of theheating.

This and further objects of the present disclosure are achieved by meansof a microwave heating apparatus and a method having the featuresdefined in the independent and dependent claims.

A microwave heating apparatus is provided. The microwave heatingapparatus comprises a cavity arranged to receive a load, a plurality offeeding ports and a control unit. The feeding ports are arranged to feedmicrowaves from a plurality of microwave generators to the cavity. Thecontrol unit is configured to obtain a desired temperature patternwithin the cavity based on information about a plurality of regions ofthe load, determine a heating pattern comprising zones of differentintensities corresponding to the desired temperature pattern and controlat least some of the plurality of microwave generators for providing thedetermined heating pattern within the cavity.

A method of heating a load in a cavity using microwaves is provided. Themethod comprises the steps of obtaining a desired temperature patternfor a plurality of regions of the load, determining a heating patternwith zones of different intensities corresponding to the desiredtemperature pattern and heating the load with the determined heatingpattern in the cavity.

The present disclosure makes use of an understanding that a heatingpattern may be obtained via control of at least some of a plurality ofmicrowave generators and that an uneven heating pattern (i.e. a heatingpattern corresponding to zones of different microwave intensities) maybe used for heating a plurality of regions of a load according to adesired temperature pattern. In the microwave heating apparatus of thepresent disclosure, information about a plurality of regions of a loadis used to determine how much different parts of the load are to beheated. A heating pattern generated by (at least some of) a plurality ofmicrowave generators is then formed, the resulting heating patterncorresponding to the desired heating of the different regions in termsof temperature.

The present disclosure is advantageous in that it provides a microwaveheating apparatus capable of heating a load depending on a desiredtemperature pattern in the load, i.e. depending on the desiredtemperatures in various parts of the load. Based on the desiredtemperature pattern, different zones of the cavity are provided withdifferent levels of microwave intensities. With the present disclosure,different desired temperatures may be obtained in various regions of theload, which is particularly advantageous if these various regions are ofdifferent types. In other words, the microwave heating apparatus of thepresent disclosure provides a zone cooking capability, i.e. thatdifferent cooking/heating is provided in different zones of the cavity.

The microwave heating apparatus of the present disclosure is a microwaveoven, but may also be a larger microwave heating apparatus forindustrial appliances or a larger microwave heating apparatus for use inautomatic vending machines.

The load may be a single food item or several food items of differenttypes, e.g. meat, potatoes and sauce. The load may consist of more orless homogeneous items such as a piece of butter, but it may also be apiece of lasagna having several different layers. The load may beconcentrated to a small part of the cavity or spread out. The load maybe large or small compared to the size of the cavity. Further, it willbe appreciated that the load may conveniently be disposed in a recipientsuch as a dish, a bowl or a cup.

The regions of the load may correspond to regions within a single fooditem or correspond to different pieces of food items. The regions of theload may be of different sizes. The regions of the load may have anypossible shape.

As mentioned above, the microwave heating apparatus of the presentdisclosure can heat loads including different items which may be heateddifferently to reach different desired finishing states or temperatures.With the present disclosure, instead of heating one item at a time,multiple items of different types can be heated simultaneously anddifferently, thereby saving both time and energy. Moreover, since theitems are heated simultaneously, none of the items will be heated firstand run the risk of cooling while the other items are heated.Simultaneous heating also increases efficiency since it reduces the needto stop heating while switching load.

The microwave heating apparatus of the present disclosure may notinclude a turntable, rotating part, or any associated motor forproviding rotation, thereby making the microwave heating apparatus ofthe present disclosure less complex and facilitating its manufacture.Moreover, the lack of rotating parts renders the microwave heatingapparatus faster to control and more adjustable to changing conditionsin the cavity.

It will be appreciated that one feeding port may be associated with oneor several microwave generators. The feeding ports may be uniformlydistributed at walls of the cavity but may also be distributed in anyother suitable way depending on the mode fields which are intended to besupported in the cavity.

The cavity may be rectangular, with e.g. several rectangular parts, butmay also be cylindrical or have any other shape suitable for heatingusing microwaves.

The desired temperature pattern may represent different desiredfinishing temperatures for the regions of the load. Since the heatingpattern is determined to comprise zones of different microwaveintensities corresponding to the desired temperature pattern, theregions of the load will then be heated to the desired finishingtemperatures. The desired temperature pattern may be obtained (at leastpartly) based on information about regions of the load. Such informationmay be obtained or derived via recognizing means, which will bedescribed in more detail in the following. The desired temperaturepattern may also represent cooking levels or desired finishing statesdirectly entered by a user for the different regions of the load. Theinformation may be entered or acquired before the heatingprogram/procedure is started and the microwave heating apparatus willthen be controlled based on such information. The information may alsobe entered or acquired during heating of the load to dynamically adjustthe heating. A change of the user's instructions during the heating mayalso be envisaged.

A burning sensor may also be used to avoid overcooking such that theheating process can be stopped when burning is detected. A cut-off tubemay be placed between any sensors and the cavity in order to preventmicrowave leakage and possible contamination of the sensors.

The plurality of microwave generators may include solid state microwavegenerators or frequency-controllable microwave generators since suchmicrowave generators enable an improved control of the heating patternin the cavity. The advantages of a solid-state microwave generatorcomprise the possibility of controlling the frequency of the generatedmicrowaves, controlling the output power of the generator and aninherent narrow-band spectrum.

The control unit may then be configured to control the frequency, thephase and/or the amplitude of the microwaves of at least some of themicrowave generators for providing the determined heating pattern. Suchcontrol is advantageous since it provides the determined heating patternwithout using moving parts and other extra equipment.

The control unit may be configured to select some of the feeding portsand microwave generators based on the determined heating pattern.Depending on the configuration and arrangement of the feeding ports, thecontrol unit may be configured to select and activate the feeding portsproviding the mode fields which, in combination, results in thedetermined heating pattern. For example, a zone of high intensity may beobtained in the cavity by combining two or more mode fields resulting inheating patterns for which the microwave intensities are added at thisparticular zone of desired high intensity. Analogously, a zone of lowintensity may be obtained by combining two or more mode fields resultingin heating patterns which cancel each other at this particular zone ofdesired low intensity. Thus, only some of the microwave generators andfeeding ports may be needed to provide the determined heating pattern.

The terms “high” and “low” above are used in a comparative manner andare not intended to correspond to a specific absolute value for thepurpose of the example, although this may be envisaged. In any case, azone of higher intensity, in comparison to other zones, in thedetermined heating pattern corresponds to a region of highertemperature, in comparison to the other regions, in the desiredtemperature pattern. A region with a higher desired temperature istherefore heated with a higher intensity, thereby improving theefficiency of the heating.

The control unit may be configured to use information about size and/orweight of the load to determine the time needed for the microwaveheating apparatus to heat various regions of the load. Optionally, thetime needed may be shown on a display as information for the user.

According to an embodiment, the control unit may be configured to obtainthe desired temperature pattern based on information about locations ofthe regions of the load within the cavity and food types correspondingto the regions of the load. Information about the type of food in aregion of the load is useful in determining a suitable finishingtemperature for the region. If the load consists, e.g., of a piece ofpie and some ice cream, it is suitable to heat the pie while keeping theice cream cool. Information about the type of food in a region of theload is to be correlated to a location of the region in the cavity inorder to obtain a desired temperature pattern and thereafter determinethe heating pattern.

According to an embodiment, the microwave heating apparatus may furthercomprise recognizing means for recognizing at least one of locations ofthe regions of the load within the cavity, food types corresponding tothe regions of the load, weights of the regions of the load, volumes ofthe regions of the load and instantaneous temperatures of the regions ofthe load. The present embodiment is advantageous in that it provides forautomatic identification of the content of the cavity and, inparticular, the load. In other words, with the recognizing means, theuser does not need to input any detailed information about the load. Themicrowave heating apparatus can automatically obtain a desiredtemperature pattern based on the information provided by the recognizingmeans (typically a set of sensors) and thereby determine a correspondingheating pattern. Information about the type of food in a region of theload is useful in determining a suitable finishing temperature for theregion. Information about the weights and/or volumes of the regions ofthe load is useful in determining how much microwave energy is needed toheat a particular region, and therefore in determining the time requiredfor heating such a region. Information about the instantaneoustemperatures of the regions of the load is useful for dynamic control ofthe heating and in particular for determining if further heating of anyof the regions is necessary, and in that case how much heating isneeded. By “instantaneous temperatures” is meant the current or presenttemperatures. It should be noted that although a short time period isalways needed to measure a temperature, the duration of this time periodis negligible compared to the heating process, whereby the measuredtemperature may be referred to as being instantaneous.

Using recognizing means, a true one touch function may be provided sincethe microwave heating apparatus is configured to automatically recognizethe content of the cavity and in particular the load. In such microwaveheating apparatus, the user may only need to select a limited number ofoptions such as the cooking program (e.g. “defrost”, “cook” and“reheat”). The microwave heating apparatus may then be able to perform asuitable heating of the load.

If the control unit has access to typical behaviors during heating ofdifferent food types (e.g. from a list stored in a memory), therecognizing means may be used to compare the evolution of the loadduring heating with expected behaviors. This may then be used asfeedback for the control unit to adjust the heating accordingly.

According to an embodiment, the microwave heating apparatus may furthercomprise an image capturing device arranged to acquire an image of theload arranged in the cavity. The control unit may then be configured toobtain the desired temperature pattern (at least partly) based on theimage. The present embodiment is advantageous in that it provides for anautomatic detection of the content of the cavity and identification ofthe load, without user input. The present embodiment is alsoadvantageous in that an image comprises much more information than whatcould reasonably be requested to be input by a user. The abundance ofinformation obtained from the image may be used to obtain a moresuitable desired temperature pattern, thereby further improving heatingperformance. It will be appreciated that the image may also be used toidentify the state of the load and thereby anticipate the cookingprogram (e.g. frozen food may be recognized and a defrosting programthereby automatically selected).

It should be noted that a plurality of image capturing devices, of thesame or different types, may be used to acquire a plurality of images,from which images the temperature pattern may be derived. Using aplurality of image capturing devices is advantageous in that the loadmay be monitored from different angles, providing a more accurate anddetailed information about the regions of the load. In particular, aplurality of cameras may be used to obtain 3D-positions of the regionsof the load within the cavity.

Optionally, the image capturing device may be used for empty cavitydetection, reducing the risk of damaging the microwave heating apparatusby heating an empty cavity. If a color camera is used as an imagecapturing device, the browning of the load may be monitored, and adesired browning level may be achieved by adjusting the heatingaccordingly.

The image capturing device may include a charge-coupled device (CCD) orany other equivalent technology such as a CMOS sensor. The sensitivityof the CCD may extend into the infrared range in order for the obtainedimages to contain information about the temperature of the regions ofthe load. Determining instantaneous temperatures of the regions of theload is useful for determining if further heating of the regions isnecessary, and in that case how much heating is needed depending on theregions. Infrared images may also be used to identify the state of theload and thereby anticipate the cooking program. For example, frozenfood may be recognized by being significantly colder than itssurrounding and a defrosting program may be selected.

According to an embodiment, the microwave heating apparatus may furthercomprise an infrared sensor for capturing a temperature image of theregions of the load and/or for identifying the location and/or shape ofthe regions of the load within the cavity. A temperature image of theregions of the load is useful for determining how much further heatingis necessary for the regions. Information about the location and/orshape of the regions of the load within the cavity may be used to obtaina desired temperature pattern suitable for the load. For the purpose ofdetermining the shape and position of regions of the load from aninfrared image, the control unit may include a processor or processingmeans capable of running a special algorithm during the initial heat-upphase of the heating program. Depending on the heat transfer occurringbetween a region of the load and its surrounding environment during theinitial heat-up phase, the control unit may then determine the shape andposition of a region of the load (e.g. shape of French fries, a piece ofmeat or a slice of pizza). In this way, the control unit may alsodetermine the corresponding food type at this position and therebyobtain a desired finishing temperature, the compilation of the desiredfinishing temperatures for different regions of the load resulting in adesired temperature pattern. Moreover, infrared images may be used toidentify the state of the load and thereby anticipate the cookingprogram. For example, frozen food may be recognized by beingsignificantly colder than its surrounding and a defrosting program maybe selected.

According to an embodiment, the microwave heating apparatus may furthercomprise entry means for entry of information comprising at least one oflocations of the regions of the load within the cavity, types of foodcorresponding to the regions of the load, weights of the regions of theload, volumes of the regions of the load, instantaneous temperatures ofthe regions of the load, desired finishing temperatures for the regionsof the load, and a selected cooking program. The present embodimentprovides an alternative to the above embodiments in which suchinformation is obtained automatically via a single sensor or a number ofsensors. The present embodiment is also advantageous in that any inputof information from a user may complete the information automaticallyobtained by such sensors. The selected cooking program is an example ofwhat might be difficult to obtain by sensors or images withoutconsulting the user. A selected cooking program may include “defrost”,“cook” or “reheat”. Any automatically selected or derived cookingprogram may, .e.g., be confirmed by a user via a user interface (buttonsor touch screen). Furthermore, the user might want to input instructionswhich would be difficult for the microwave heating apparatus toanticipate (e.g. heating water to a certain temperature or heating foodintended for children to a lower temperature).

According to an embodiment, the control unit may be configured tocontrol some of the microwave generators for simultaneous feeding ofmicrowaves to the cavity. The present embodiment is advantageous in thatthe addition of heating patterns provided by microwaves originating fromdifferent microwave generators (and feeding ports) may result in aheating pattern that would be more difficult or even impossible toobtain with microwaves originating from a single microwave generator(and feeding port) at a time, without using moving parts or advancedfeeding systems.

According to an embodiment, the plurality of microwave generators mayinclude magnetrons, and the control unit may be configured to controlsome of the magnetrons for feeding of microwaves to the cavity duringdifferent time periods. Using different time periods, the microwavesfrom the different magnetrons will not interfere with each other and canperform independently. The time periods during which the microwaves fromdifferent magnetrons are fed to the cavity are short compared to theheating process, thereby ensuring that the heating process evolves as ifa single heating pattern was applied to the load.

According to an embodiment, the microwave heating apparatus may furthercomprise a display screen for displaying the load located in the cavityand entry means for selection of a cooking level for the regions of theload, the temperature pattern corresponding to the selected cookinglevel. In the present embodiment, the user may directly see where theload, or a region of the load, is located in the cavity and may choosehow such a region of the load is to be heated. An advantage of using adisplay screen is that there is no need for a window at a wall of thecavity for observation of the load. Not using such windows isadvantageous since they usually require a shield for minimizingmicrowave leakage and may also affect the heating patterns in thecavity.

According to an embodiment, the obtaining (of a desired heating pattern)is performed before the start of a heating procedure. This means that adesired temperature pattern is obtained before the load is subjected toheating by the microwave heating apparatus, which is advantageousbecause the determined heating pattern may then be used already from thestart, improving the efficiency of the heating.

According to an embodiment, the obtaining (of a desired heating pattern)is performed during a heating procedure. This means that a desiredtemperature pattern is obtained during heating of the load. The presentembodiment is advantageous in that the determined heating pattern may bealtered during the heating procedure, compensating for events and factsthat evolve during the heating procedure (such as a change of state of aregion of the load) or that were unknown before the start of the heatingprocedure. For example, the status of the load may be monitored duringheating and new desired heating patterns may be obtained each timecertain predetermined conditions are met (e.g. that a certain time haselapsed or that a region of the load has reached a certain temperature).

It will be appreciated that any of the features in the embodimentsdescribed above for the microwave heating apparatus according to thefirst aspect of the present disclosure may be combined with theembodiments of the method according to the second aspect of the presentdisclosure. Similarly, it will be appreciated that any of the featuresin the embodiments described above for the method according to thesecond aspect of the present disclosure may be combined with theembodiments of the microwave heating apparatus according to the firstaspect of the present disclosure.

Further objectives of, features of, and advantages with, the presentdisclosure will become apparent when studying the following detaileddisclosure, the drawings and the appended claims. Those skilled in theart will realize that different features of the present disclosure canbe combined to create embodiments other than those described in thefollowing.

BRIEF DESCRIPTION OF THE DRAWINGS

The above, as well as additional objects, features and advantages of thepresent disclosure, will be better understood through the followingillustrative and non-limiting detailed description of preferredembodiments of the present disclosure, with reference to the appendeddrawings, in which:

FIG. 1 schematically shows a microwave heating apparatus according to anembodiment of the present disclosure;

FIG. 2 schematically shows a microwave heating apparatus according toanother embodiment of the present disclosure;

FIGS. 3a-c are schematic top views of the cavity of the microwaveheating apparatus shown in FIGS. 1 and 2, which top views schematicallyshow a plurality of regions of a load (FIG. 3a ), an associated desiredtemperature pattern (FIG. 3b ) and a corresponding heating pattern (FIG.3c ); and

FIG. 4 is a general outline of a method of heating a load usingmicrowaves in accordance with an embodiment present disclosure.

All the figures are schematic, not necessarily to scale, and generallyonly show parts which are necessary in order to elucidate thedisclosure, wherein other parts may be omitted or merely suggested.

DETAILED DESCRIPTION

With reference to FIGS. 1 and 3 a-c, a microwave heating apparatusaccording to an embodiment of the present disclosure is described.

FIG. 1 shows a microwave heating apparatus 100 comprising a cavity 101arranged to receive a load 102. The microwave heating apparatus 100 isequipped with a plurality of feeding ports 103 a-d for feedingmicrowaves from a plurality of microwave generators 104 a-b to thecavity 101. The microwave heating apparatus 100 is also equipped with acontrol unit 105 configured to obtain a desired temperature pattern 301within the cavity 101 based on information about a plurality of regions302 a-h of the load 102, determine a heating pattern 303 comprisingzones 304 of different intensities corresponding to the desiredtemperature pattern 301 and control at least some of the plurality ofmicrowave generators 104 a-b for providing the heating pattern 303within the cavity 101.

For feeding microwaves from the microwave generators 104 a-b to thecavity 101, the microwave heating apparatus 100 may also be equippedwith transmission lines 106. The transmission lines 106 are arrangedbetween the microwave generators 104 a-b and the cavity 101 for feedingof microwaves via the feeding ports 103 a-d. The microwave generators104 a-b are arranged at the respective first ends, or extremities, ofthe transmission lines 106 while the cavity 101 is arranged at thesecond ends, opposite to the first ends, of the transmission lines 106.The microwave generators 104 a-b are adapted to generate microwaves,e.g. via their respective antennas (not shown), and the transmissionlines 106 are configured to transmit the generated microwaves from the(antenna of the) microwave generators 104 a-b to the cavity 101. Thetransmission lines 106 may be waveguides or coaxial cables.

In general, each of the microwave generators 104 a-b may be associatedwith a dedicated feeding port 103 a-d (and possibly with a dedicatedtransmission line 106) such that the power of the microwaves transmittedfrom each of the microwave generators 104 a-b and, optionally, the powerof the microwaves reflected to each one of the microwave generators 104a-b can be separately monitored.

A feeding port 103 a-d may for instance be an antenna, such as a patchantenna or an H-loop antenna, or even an aperture in a wall (includingsidewalls, the bottom and the ceiling) of the cavity 101. In thefollowing, all these possible alternatives will be referred to simply asfeeding ports.

In the present embodiment, there are two microwave generators 104 a-bmounted on the outside of the walls of the cavity 101. The cavity orenclosure 101 has the shape of a rectangular parallelepiped, i.e. ashape similar to that of a box but with rectangles as faces instead ofsquares. One of the microwave generators 104 a is mounted on the rightwall of the cavity 101 and is connected by transmission lines 106 to twofeeding ports 103 a-b located at the right wall of the cavity 101. Oneof these feeding ports 103 a is located in the upper part of the rightwall, preferably centered along the horizontal direction of the wallwhile the other one of these feeding ports 103 b is located in the lowerpart of the right wall, preferably centered along the horizontaldirection of the wall. The second microwave generator 104 b is mountedon the bottom wall of the cavity 101 and connected by transmission lines106 to two feeding ports 103 c-d located at the bottom wall of thecavity 101. One of these feeding ports 103 c is located in the left partof the bottom wall, preferably centered similarly to the feeding ports103 a-b along the right wall. The other one of these feeding ports 103 dis located in the right part of the bottom wall, preferably centeredsimilarly to the feeding ports 103 a-b along the right wall.

The arrangement of feeding ports 103 a-d and microwave generators 104a-b described herein with reference to FIG. 1 is only provided as anexample and is not limiting. It will be appreciated that more than twomicrowave generators 104 a-b may be provided and also that the microwaveheating apparatus 100 may include even more feeding ports 103 a-d toprovide flexibility in providing different heating patterns.

The cavity 101 of the microwave heating apparatus 100 defines anenclosing surface wherein one of the side walls of the cavity 101 may beequipped with a door (not shown in FIG. 1, but the door may suitably bearranged at the open side of the depicted cavity 101) for enabling theintroduction of a load 102, e.g. a food item, in the cavity 101.

The microwaves generated by a microwave generator 104 a-b and fed to thecavity 101 via its respective feeding ports 103 a-d provide a mode fieldin the cavity 101. Mode fields provided by several microwave generators104 a-b may be combined to form a heating pattern in the cavity 101.

In general, the number and/or type of available mode fields in a cavityare determined by the design of the cavity. The design of a cavitycomprises the physical dimensions of the cavity and the location of thefeeding port(s) in the cavity. The dimensions of the cavity aregenerally provided by its height, depth and width. Further, whendesigning a cavity of a microwave heating apparatus, the impedancemismatch created between any transmission line and the cavity may betaken into account. For this purpose, the length of the transmissionlines may also be slightly adjusted and the dimensions of the cavitytuned accordingly. During the tuning procedure, a load simulating atypical load to be arranged in the cavity may be present in the cavity.In addition, the tuning may be accomplished via local impedanceadjustments, e.g., by introduction of a tuning element (such as acapacitive post) arranged in the transmission line or in the cavity,adjacent to the feeding port.

Advantageously, the control unit 105 may comprise, or may have thepossibility to access, a look-up table or memory in which a number ofparameters to operate (at least some of) the microwave generators 104a-b are known in order to obtain a specific heating pattern for typicalloads 102. From such a look-up table, the control unit 105 may derive orcompute the required microwave generators 104 a-b and feeding ports 103a-d (and their operating parameters) in order to achieve a particularheating pattern (corresponding to a desired temperature pattern 301).

In general, the feeding ports 103 a-d may be arranged at, in principle,any walls of the cavity 101. However, there is generally an optimizedlocation of the feeding ports for a predefined mode field.

In the present embodiment, the cavity is designed to have the shape of arectangular parallelepiped, e.g., with a width with order of about450-500 mm, a depth of about 400 mm and a height of approximately 400mm. However, this is just an example of the shape and size of the cavity101. The cavity 101 may have many different shapes, such as apolyhedron, a cylinder, a sphere, etc. or combinations thereof.

In the present embodiment, the microwave heating apparatus 100 isequipped with an image capturing device 107 arranged to acquire an imageof the load 102 arranged in the cavity 101. The image capturing device107 is arranged to view the cavity 101 and the load 102 from above,acquiring images as that shown in FIG. 3a . The sensitivity of the imagecapturing device may extend into the infrared range and, in such case,the microwave heating apparatus may include a processor or processingmeans for filtering the information obtained by the image capturingdevice. In particular, the processor may be configured to filter theinformation (or signal) to reconstitute an image corresponding to theinfrared part of the sensitivity of the device and another imagecorresponding to the visible part of the sensitivity of the device. Theprocessor may be part of the image capturing device or part of thecontrol unit of the microwave heating apparatus. The filtering functionof such processor is capable of distinguishing the part of the signaloriginating from the infrared part of the spectrum from the part of thesignal originating from the visible part of the spectrum. The imagecapturing device 107 may be mounted in a centralized position along theupper wall of the cavity 101, for having a good view of the interior ofthe cavity 101. The image capturing device 107 may include acharge-coupled device, but may also include infrared sensors dependingon the type of image to be acquired.

In the present embodiment, the control unit 105 is arranged on theoutside of the left wall of the cavity 101. The control unit 105 may beconnected by wires 108 to the microwave generators 104 a-b forcontrolling them and to the image capturing device 107 for receivinginformation about the load 102. The wires 108 may be replaced by otherelectrical connection means or even wireless communication.

In general, the image acquired by the image capturing device 107 mayeither be sent directly to the control unit 105 using the wires 108 (orwireless communication) for subsequent analysis of the image, or theimage capturing device 107 may comprise image processing means forextracting information from the image, which information may then besent to the control unit 105.

In the present embodiment, the image is sent as a digital signal to thecontrol unit 105 which is equipped with a processor for acquiringinformation from the image. Using a grid 311, the control unit 105 maydivide the image into a plurality of square-shaped regions representingregions 302 a-h of the load 102. This is just an example of how an imagemay be divided into regions. Another possibility would be to divide theimage using concentric circles and lines starting at the center of thecircles in order to form a pattern similar to that of a dart board.Since the regions of the load may be of any possible shape, there aremany different ways to divide the image into regions.

The image capturing device 107 may be placed at any location along thewalls of the cavity 101 in order to acquire images of the cavity 101from different angles. These images may be used to distinguish theregions 302 a-h of the load 102. Depending on the angle at which theimages are acquired, the regions 302 a-h of the load 102 may havedifferent geometries. Moreover, a plurality of images acquired fromdifferent angles by different image capturing devices 107 may becombined to form a three-dimensional representation of the load 102,which representation may be used to define the regions 302 a-h of theload 102.

In the present example, the load 102 may comprise a piece of pie 305, apiece of meat 306 and a piece of bread 307, all placed on a plate 308 inthe cavity 101. The square-shaped regions of the image in which the foodlies represent the different regions 302 a-h of the load 102. Inparticular, the regions denoted 302 a-c correspond to parts of the bread307, the regions denoted 302 e-f correspond to parts of the piece ofmeat 306 and the regions denoted 302 g-h correspond to parts of thepiece of pie 305. The square-shaped regions of the image not overlappingthe food are not considered to represent any regions 302 a-h of the load102, but instead correspond to parts of the cavity being empty (orpossibly containing parts of the plate 308 which is not supposed to beheated).

Based on the image acquired by the image capturing device 107,information about the regions 302 a-h of the load 102 may be derived. Inthe present embodiment, the image capturing device 107 includes acharge-coupled device whose sensitivity may extend into the infraredrange. Thereby, the derived information may comprise information aboutthe location in the cavity 101 of the regions 302 a-h of the load 102,the food type of the regions 302 a-h of the load 102 and the presenttemperature of the regions 302 a-h of the load 102. Indeed, the foodtype may be determined based on the appearance of the food in the image,especially if the possible food types in the load are few and ofdifferent appearance. For example, the control unit 105 may comprise amemory in which a plurality of food types and associated visualappearances are listed. Comparing the regions 302 a-h of the load 102with such a list using image processing techniques, the control unit 105may determine which food type is most likely to be present in eachregion 302 a-h of the load 102.

Using the food type of a region 302 a-h, the control unit 105 may thenobtain a suitable finishing temperature or surface browning. Forexample, the control unit 105 may comprise a memory in which suitablefinishing temperatures of different food types are stored. For thispurpose, the control unit 105 may also be adapted to obtain a desiredcooking level or cooking program, either via the image capturing device107 or via user entry (further explained below). Based on the desiredfinishing temperatures of the different regions 302 a-h of the load 102,the control unit 105 may obtain a desired temperature pattern 301.Alternatively, the desired temperature of a region 302 a-h is comparedwith the present temperature of that region 302 a-h and the desiredtemperature pattern is then based on how much each region 302 a-h needsto be heated in order to reach its desired finishing temperature, i.e.the temperature pattern may not be based solely on the desired finishingtemperatures.

In FIG. 3b the desired temperature pattern 301 is visualized by acoloring of the regions 302 a-h of the load 102 using a grayscale. Thepiece of pie is cold and the associated regions 302 g-h need to beheated to a high extent. This is represented in the desired temperaturepattern 301 by a coloring of the regions 302 g-h of the load by a darkshade of gray 309. The piece of meat 306, on the other hand, is alreadyquite warm, so the associated regions 302 d-f only need to be heated alittle. This is represented in the desired temperature pattern 301 by acoloring of the regions 302 d-f of the load 102 by a bright shade ofgray 310. The piece of bread 307 is not frozen, so the associatedregions 302 a-c do not need to be heated. This is represented in thedesired temperature pattern 301 by the fact that there is no coloring ofthe regions 302 a-c of the load 102.

In the present example, the desired temperature pattern 301 representssome kind of differential temperature pattern, i.e. how much aparticular region needs to be heated, which then corresponds to thedifference between the desired finishing temperature at a location andthe current temperature of the load at this location.

However, in a simpler manner, the desired temperature pattern maydirectly correspond to the absolute desired finishing temperatures atthe various regions of the load (i.e. not corresponding to a differencebetween such desired finishing temperature and a current temperature).Any necessary computation of the difference may be made by the controlunit 105 just before determining the heating pattern.

Using the desired temperature pattern 301, the control unit 105determines a heating pattern 303 with zones 304 of differentintensities, suitable for heating the load 102 properly. For thispurpose, the control unit 105 may comprise a memory in which differentpossible mode fields of the microwave generators 104 a-b and associatedfeeding ports 103 a-d are stored. In this memory, there may also bestored information about how these mode fields may be combined to formdifferent heating patterns in the cavity 101. By comparing the desiredtemperature pattern 301 with heating patterns that may be obtained bycombining the stored mode fields, the control unit may determine asuitable heating pattern 303 with zones 304 of different intensitiescorresponding to the desired temperature pattern 301.

In FIG. 3c the determined heating pattern 303 is visualized by zones 304colored by different shades of gray, representing different heatingintensities corresponding to the piece of pie 305 and the piece of meat306. It will be appreciated that the determined heating pattern 303 isnot exactly similar to the desired temperature pattern 301 simplybecause it represents a heating pattern obtainable from mode fieldsavailable via the microwave generators 104 a-b and the associatedfeeding ports 103 a-d of cavity 101. Still, the determined heatingpattern 303 matches the desired temperature pattern 301, therebyproviding the desired heating of the load 102.

A zone 304 of the determined heating pattern 303 may correspond to manyregions 302 a-h of the load 102 with similar desired heating, i.e. thenumber of zones 304 may be much lower than the number of regions 302 a-hof the load 102. In the present embodiment, all regions 302 a-c of theload corresponding to the piece of pie 305 correspond to a single zone304 in the determined heating pattern 303.

The control unit 105 then controls the different microwave generators104 a-b and the associated feeding ports 103 a-d to provide mode fieldsthat together form the determined heating pattern 303. Thereby, the load102 is heated.

According to an embodiment, the microwave generators 104 a-b may besolid-state microwave generators including e.g. a varactor diode (havinga voltage-controlled capacitance). Solid-state based microwavegenerators may, for instance, comprise silicon carbide (SiC) or galliumnitride (GaN) components. Other semiconductor components may also beadapted to constitute the microwave generators 104 a-b. In addition tothe possibility of controlling the frequency of the generatedmicrowaves, the advantages of a solid-state based microwave generatorcomprise the possibility of controlling the output power level of thegenerator and an inherent narrow-band feature. The frequencies of themicrowaves that are emitted from a solid-state based generator usuallyconstitute a narrow range of frequencies such as 2.4 to 2.5 GHz.However, the present disclosure is not limited to such a range offrequencies and the solid-state based microwave generators could beadapted to emit in a range centered at 915 MHz, for instance 875-955MHz, or any other suitable range of frequency (or bandwidth). Theembodiments described herein are for instance applicable for standardgenerators having mid-band frequencies of 915 MHz, 2450 MHz, 5800 MHzand 22.125 GHz. Alternatively, the microwave generators 104 a-b may befrequency-controllable magnetrons such as disclosed in documentGB2425415.

The use of solid state microwave generators or frequency-controllablemicrowave generators is advantageous in that it provides a highlyadjustable heating pattern without the need of moving parts. Theamplitude, the frequency and the phase of the microwaves emitted fromthe microwave generators 104 a-b may be adjusted. Adjustment of theaforementioned parameters in the power supplies will affect theresulting heating patterns, thereby providing the possibility ofadjusting the heating pattern provided in the cavity even moreaccurately and improving the matching between the determined heatingpattern 303 and the desired temperature pattern 301.

For the purpose of regulation, the control unit 105 may be configured tocontrol the frequency, the phase and/or the amplitude of the power fromat least one of the microwave generators 104 a-b for adjusting theheating pattern provided in the cavity 101. The microwave generators 104a-b may be independently controlled and independently operable.

Still for the purpose of regulation, the control unit 105 may beconfigured to receive information about measurements of the amount ofmicrowaves reflected from the cavity 101.

The microwave heating apparatus shown in FIG. 2 is similar to that shownin FIG. 1. The present microwave heating apparatus is a microwave ovenfor heating food items. As compared to the microwave heating apparatusdescribed with reference to FIGS. 1 and 3 a-h, the microwave oven 100shown in FIG. 2 further comprises means 201 for entry of informationsuch as locations of the regions 302 a-h of the load 102 within thecavity 101, types of food corresponding to the regions 302 a-h of theload 102, weights of the regions 302 a-h of the load 102, volumes of theregions 302 a-h of the load 102, instantaneous temperatures of theregions 302 a-h of the load or desired finishing temperatures for theregions 302 a-h of the load 102 or a selected cooking program.

The microwave oven 100 has a front door with a window for allowing theuser to see the load 102 arranged in the cavity 101. The means 201 forentry of information is located above the window and comprises aplurality of buttons that may be used by the user to enter informationabout the load 102 and how it should be heated. The user may enterinformation about the regions 302 a-h of the load 102, one afteranother, indicating which type of information is being entered and towhich region 302 a-h of the load the information is supposed to beassociated. The entered information is sent by electrical connectionmeans to the control unit 105 which optionally may combine thisinformation with information gathered from the image obtained by theimage capturing device 107 in order to obtain a desired temperaturepattern 301.

In the present embodiment, the microwave oven 100 further comprises adisplay screen 202 for displaying the load 102 located in the cavity101. The display screen 202 is located above the window and may be atouch sensitive screen. In that case, the display screen 202 may also beused for entry of information. For example, the user may press certainparts of the display screen 202 corresponding to regions 302 a-h of theload 102, to indicate that new information about these regions 302 a-hof the load 102 will be entered. The user may then use the means 201 forentry (the buttons) to input information about the indicated regions 302a-h of the load 102. Alternatively, a menu for selection of options mayopen on the touch screen, thereby enabling selection of, e.g., finishingtemperature or state (or even cooking level such as “well done” or“medium rare” for a piece of meat.)

With reference to FIG. 4, a method for heating a load using microwavesis described in accordance with an embodiment of the present disclosure.The same reference numbers as for the features of the microwave heatingapparatus described with reference to FIGS. 1 and 3 a-h are used in thefollowing.

The method comprises the step 401 of obtaining a desired temperaturepattern 301 for a plurality of regions 302 a-h of the load 102, the step402 of determining a heating pattern 303 with zones 304 of differentintensities corresponding to the temperature pattern 301, and the step403 of heating the load 102 with the determined heating pattern 301 inthe cavity 101.

Further, it will be appreciated that any one of the embodimentsdescribed above with reference to FIGS. 1, 2 and 3 a-c is combinable andapplicable to the method described herein with reference to FIG. 4.

The present disclosure is applicable for domestic appliances such as amicrowave oven using microwaves for heating. The present disclosure isalso applicable for larger industrial appliances found in, e.g., foodoperation. The present disclosure is also applicable for vendingmachines or any other dedicated applications.

While specific embodiments have been described, the skilled person willunderstand that various modifications and alterations are conceivablewithin the scope as defined in the appended claims.

For example, although the microwave heating apparatus 100 described withreference to the FIGS. 1, 2 and 3 a-c comprise two microwave generators104 a-b and four feeding ports 103 a-d, it will be appreciated thatthese numbers are just examples, by no means limiting the differentpossible combinations of microwave generators 104 a-b and feeding ports103 a-d.

The invention claimed is:
 1. A microwave heating apparatus comprising: acavity arranged to receive at least one load having load regions; aplurality of independently controllable microwave generators; aplurality of feeding ports configured to feed microwaves from theplurality of microwave generators to the cavity, wherein the microwavesprovide mode fields in the cavity; and a control unit configured to:obtain a desired temperature pattern for the at least one load based oninformation about the load regions; determine a heating pattern in thecavity comprising zones of different intensities corresponding to thedesired temperature pattern, wherein a zone of higher intensity in thedetermined heating pattern corresponds to a region requiring highertemperature in the desired temperature pattern; and control at least oneof the plurality of independently controllable microwave generators orthe plurality of feeding ports so the mode fields form the determinedheating pattern and thereby heat the at least one load according to thedesired temperature pattern.
 2. The microwave heating apparatus of claim1, wherein the control unit is configured to receive information aboutmeasurements of the amount of microwaves reflected from the cavity andat least one of the plurality of independently controllable microwavegenerators or the plurality of feeding ports based also on thatinformation.
 3. The microwave heating apparatus of claim 1, wherein theinformation about the load regions includes at least one of the locationof the load regions within the cavity, a food type corresponding to theload regions, a weight of the load regions, a volume of the load regionsor an instantaneous temperature of the load regions.
 4. The microwaveheating apparatus of claim 1, further comprising an image capturingdevice arranged to acquire an image of the load arranged in the cavitywherein the control unit is further configured to derive the informationabout the load regions from the image.
 5. The microwave heatingapparatus of claim 4, wherein the image capturing device includes acharge-coupled device whose sensitivity extends into the infrared range.6. The microwave heating apparatus of claim 1, wherein the desiredtemperature pattern represents different desired finishing temperaturesfor different load regions.
 7. The microwave heating apparatus of claim1, further comprising an infrared sensor for capturing a temperatureimage of the load regions wherein the control unit is further configuredto derive the information about the load regions from the temperatureimage.
 8. The microwave heating apparatus of claim 1, further comprisingan entry means for user entry of at least a portion of the informationabout the load regions.
 9. The microwave heating apparatus of claim 8,wherein the entry means includes a touch screen display for displayingthe load located in the cavity and for selection of a cooking level forthe load regions, the temperature pattern corresponding to the selectedcooking level.
 10. The microwave heating apparatus of claim 1, whereinthe control unit is configured to control at least one of a frequency, aphase or an amplitude of the microwaves of at least some of themicrowave generators for providing the determined heating pattern. 11.The microwave heating apparatus of claim 1, wherein the plurality ofmicrowave generators includes at least one of a solid state microwavegenerator or a frequency-controllable magnetron.
 12. The microwaveheating apparatus of claim 1, wherein the control unit is configured tocontrol some of the microwave generators for simultaneous feeding ofmicrowaves to the cavity.
 13. The microwave heating apparatus of claim1, wherein the plurality of microwave generators includes magnetrons,the control unit being configured to control some of the magnetrons forfeeding of microwaves to the cavity during different time periods. 14.The microwave heating apparatus of claim 1, wherein the control unit isconfigured to select some of the feeding ports and microwave generatorsbased on the determined heating pattern.
 15. A microwave heatingapparatus comprising: a cavity configured to receive a load; at leastone microwave port configured to supply a signal from at least onesignal generator to the cavity, the signal being generated by at leastone of a solid state microwave generator or a frequency-controllablemagnetron, wherein the signal is configured to provide a mode field inthe cavity; and a control unit, wherein the control unit is configuredto obtain a desired temperature pattern within the cavity based on atleast one sensed input in at least one region of the load to determine aheating pattern correlating to the desired temperature pattern andcomprising a plurality of zones having different intensities, theintensities corresponding to the desired temperature pattern, wherein azone of higher intensity in the determined heating pattern correspondsto a region of higher temperature in the desired temperature pattern;and wherein the control unit is configured to control at least one of aplurality of signals generated by the signal generator for combiningmode fields provided by at least one of the signal generators therebyproviding the heating pattern within said cavity.
 16. The microwaveheating apparatus of claim 15, wherein the desired temperature patternis based on at least one of a location of the load regions, a food typecorresponding to the load regions, a weight of the load regions, avolume of the load regions or an instantaneous temperature of the loadregions within the cavity.
 17. The microwave heating apparatus of claim15, further comprising an image capturing device configured to acquirean image of the load arranged in the cavity, the control unit beingconfigured to obtain the desired temperature pattern based on the image.18. The microwave heating apparatus of claim 15, further comprising aninfrared sensor for at least one of capturing a temperature image of theload regions wherein the control unit is further configured to deriveinformation about the load regions from the temperature image.
 19. Themicrowave heating apparatus of claim 15, further comprising an entrymeans for user entry of at least one of a location of the load regions,a food type corresponding to the load regions, a weight of the loadregions, a volume of the load regions, an instantaneous temperature ofthe load regions, a desired finishing temperature for the load regionswithin the cavity, or a selected cooking program from a set of cookingprograms wherein the control unit is further configured to correlate thedesired temperature pattern and the determined heating pattern based onthe user entry.